Revert of Break page load metrics test dependency on IPC.

Revert of Break page load metrics test dependency on IPC. (patchset #2 id:20001 of https://codereview.chromium.org/2847513002/ )

Reason for revert:
PageLoadMetricsBrowserTest.DocumentWriteReloada is flaky

https://luci-milo.appspot.com/buildbot/chromium.memory/Linux%20MSan%20Tests/387

Original issue's description:
> Break page load metrics test dependency on IPC.
> 
> This change breaks direct dependencies on IPC for page load metrics
> tests, in order to ease the transition to mojo.
> 
> Previously, unit tests exercised the IPC dispatch path. This
> achieved slightly increased coverage but coupled unit tests to
> IPC. We now dispatch simulated timing events directly to callbacks,
> bypassing the IPC dispatch.
> 
> Additionally, we break the browsertest dependency on IPC and add
> a MetricsWebContentsObserver::TestingObserver, which can observe
> state changes at the observer level, instead of watching for IPC
> messages. This both simplifies the logic and more directly verifies
> expected behavior at the appropriate level.
> 
> BUG=715744
> TBR=csharrison
> 
> Review-Url: https://codereview.chromium.org/2847513002
> Cr-Commit-Position: refs/heads/master@{#467687}
> Committed: https://chromium.googlesource.com/chromium/src/+/9567f9fa3fcfcaa50fc7b6a6adf66106a2eb6be5

TBR=lpy@chromium.org,bmcquade@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=715744
Review-Url: https://codereview.chromium.org/2847803002
Cr-Commit-Position: refs/heads/master@{#467691}
Committed: https://chromium.googlesource.com/chromium/src/+/2cb37fe0beb13e6baa8852662362e9204d1ebfa3

[zmin, 2017-04-27 15:43:21]

The CQ bit was checked by zmin@chromium.org

[zmin, 2017-04-27 15:43:21]

Created Revert of Break page load metrics test dependency on IPC.

[commit-bot: I haz the power, 2017-04-27 15:44:17]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-27 15:45:27]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1493307801062350, "parent_rev":
"dccdf8bfe040e02eb4944fb1a2767ace9a32ce45", "commit_rev":
"2cb37fe0beb13e6baa8852662362e9204d1ebfa3"}

[commit-bot: I haz the power, 2017-04-27 15:45:41]

Description was changed from

==========
Revert of Break page load metrics test dependency on IPC. (patchset #2 id:20001
of https://codereview.chromium.org/2847513002/ )

Reason for revert:
PageLoadMetricsBrowserTest.DocumentWriteReloada is flaky

https://luci-milo.appspot.com/buildbot/chromium.memory/Linux%20MSan%20Tests/387

Original issue's description:
> Break page load metrics test dependency on IPC.
> 
> This change breaks direct dependencies on IPC for page load metrics
> tests, in order to ease the transition to mojo.
> 
> Previously, unit tests exercised the IPC dispatch path. This
> achieved slightly increased coverage but coupled unit tests to
> IPC. We now dispatch simulated timing events directly to callbacks,
> bypassing the IPC dispatch.
> 
> Additionally, we break the browsertest dependency on IPC and add
> a MetricsWebContentsObserver::TestingObserver, which can observe
> state changes at the observer level, instead of watching for IPC
> messages. This both simplifies the logic and more directly verifies
> expected behavior at the appropriate level.
> 
> BUG=715744
> TBR=csharrison
> 
> Review-Url: https://codereview.chromium.org/2847513002
> Cr-Commit-Position: refs/heads/master@{#467687}
> Committed:
https://chromium.googlesource.com/chromium/src/+/9567f9fa3fcfcaa50fc7b6a6adf6...

TBR=lpy@chromium.org,bmcquade@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=715744
==========

to

==========
Revert of Break page load metrics test dependency on IPC. (patchset #2 id:20001
of https://codereview.chromium.org/2847513002/ )

Reason for revert:
PageLoadMetricsBrowserTest.DocumentWriteReloada is flaky

https://luci-milo.appspot.com/buildbot/chromium.memory/Linux%20MSan%20Tests/387

Original issue's description:
> Break page load metrics test dependency on IPC.
> 
> This change breaks direct dependencies on IPC for page load metrics
> tests, in order to ease the transition to mojo.
> 
> Previously, unit tests exercised the IPC dispatch path. This
> achieved slightly increased coverage but coupled unit tests to
> IPC. We now dispatch simulated timing events directly to callbacks,
> bypassing the IPC dispatch.
> 
> Additionally, we break the browsertest dependency on IPC and add
> a MetricsWebContentsObserver::TestingObserver, which can observe
> state changes at the observer level, instead of watching for IPC
> messages. This both simplifies the logic and more directly verifies
> expected behavior at the appropriate level.
> 
> BUG=715744
> TBR=csharrison
> 
> Review-Url: https://codereview.chromium.org/2847513002
> Cr-Commit-Position: refs/heads/master@{#467687}
> Committed:
https://chromium.googlesource.com/chromium/src/+/9567f9fa3fcfcaa50fc7b6a6adf6...

TBR=lpy@chromium.org,bmcquade@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=715744

Review-Url: https://codereview.chromium.org/2847803002
Cr-Commit-Position: refs/heads/master@{#467691}
Committed:
https://chromium.googlesource.com/chromium/src/+/2cb37fe0beb13e6baa8852662362...
==========

[commit-bot: I haz the power, 2017-04-27 15:45:43]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/2cb37fe0beb13e6baa8852662362...

[Bryan McQuade, 2017-04-27 15:52:13]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2849563002/ by bmcquade@chromium.org.

The reason for reverting is: The flake that caused the previous revert by zmin
existed before the original patch landed, so the original patch is not the cause
of the flake.

This refactor should help us to un-flake the test, so I'm re-landing it..